The present invention is directed to devices that are used to facilitate post-operative bone-to-bone fusion, tissue-to-bone fusion and particularly, bone fusion between two adjacent vertebrae.
Vertebral disc degeneration has been associated with back pain and motor function loss. Loss of disc space height, extrusion of disc material, and translation of the vertebrae can result in compression of the spinal cord and nerve roots. One prescriptive treatment is to stabilize the vertebral bodies through fusion of adjacent vertebrae within the spinal column.
An operative technique of spinal column fusion employs inter-vertebral body cages. Available in different configurations from several manufacturers, the cage is inserted between two vertebral bodies in order to restore space between the discs. The device is filled with bone graft to promote fusion between the vertebrae. Access holes around the periphery of the cage provide intimate contact between the graft and host bone. The cages are typically inserted from the back (posterior) or front (anterior) aspects of the spinal column. The anterior approach involves laparoscopic methods.
Stabilization of the fusion site is advantageous in the early post-operation period. Similar to fracture healing, new bone is overlayed between the vertebral bodies, using the graft material as a lattice. Using cages as stand alone devices has met with limited success for the reason that immediate stabilization is not always guaranteed. For this reason, supplemental fixation is becoming more commonplace.
One current stabilization technique employs the placement of fixed translaminar screws into a hole drilled through adjacent vertebrae. FIGS. 1A and 1B show typical lumbar vertebrae in which translaminar screws are driven across the facet joint, effectively locking the two vertebrae in place while allowing for the four types of spine motion: forward flexion, backwards extension, axial torsion, and lateral flexion.
There is an ongoing need to provide for a facet fixation device that can be delivered simply, accurately, and quickly, while providing performance that is superior or equal to that of screw fixation.
In one aspect, the present invention is an expandable sleeve deployable in a surgical implant. The sleeve has a head, a tubular shaft defining an open interior, and a distal tip, with the shaft having a length dimension. The shaft is provided with a plurality of slots that divide the shaft into partitions, wherein each of the partitions has a length, and the length of the partitions are not all equal. For example, the slots may have a curved portion that extends at an angle between 0xc2x0 and 90xc2x0 to the length dimension of the shaft. The slots may also have a straight portion and a curved portion.
In yet another embodiment, the expandable sleeve has an open interior that is provided with a first zone proximate the head which has a first cross sectional area and a second zone proximate the distal tip that has a second cross sectional area, wherein the first cross sectional area is greater than the second cross sectional area. In yet another embodiment, the expandable sleeve has a third zone positioned intermediate the first zone and second zone, the third zone having a varying cross sectional area that decreases incrementally moving from the first zone to the second zone.
In yet another embodiment, the slots of the expandable sleeve extend from a midsection of the shaft to a terminal location on the shaft that is short of the distal tip. In another embodiment, the head extends outward from the shaft and is provided with teeth facing the distal tip. In yet another embodiment, the head of the expander pin extends outward from the shaft and has a convex distal tip.
In yet another embodiment, the head of the expandable sleeve is provided with a recess for receiving a bushing. The recess may be provided with a tapered profile that varies in cross sectional area over a length dimension.
In yet another embodiment, the slots divide the shaft into a first slot half and a second slot half, with the length dimension of the first half being greater than the length dimension of the second half. In yet another embodiment, the shaft of the expandable sleeve is provided with additional slots that divide the shaft into four quarters, wherein the length dimension of two quarters is greater than the length dimension of the two other quarters.
In yet another embodiment, the shaft of the expandable sleeve is provided with fenestrations on an exterior side. The fenestrations may vary in their length as measured in a radial dimension of the sleeve.
In yet another embodiment the present invention is a surgical implant having an expandable sleeve having any of the features as aforedescribed, and an expander pin comprised of a head and a shaft positioned within the open interior of the sleeve. The cross sectional area of the expander pin is larger than cross sectional area of at least a portion of the cross sectional area of the open interior, so that when the expandable pin is moved through the open interior, the expandable sleeve expands at the slots.
The expander pin has a distal tip and an end opposite the head, wherein the shaft is provided with a first zone proximate the head having a first cross sectional area and a second zone proximate the distal tip having a second cross sectional area, wherein the second cross sectional area is greater than the first cross sectional area.
In a further embodiment, the surgical implant is further provided with a bushing that resides in a cavity positioned within the open interior of the sleeve, located proximate the opening of the sleeve. The bushing has a shaped portion and a flange portion extending outward of the shaped portion, the bushing further provided with a through-channel dimensioned to receive the pin, and a discontinuation in the bushing, the channel being sized the same as or substantially the same as the pin, wherein the cavity is provided with dimensions complimentary to the dimensions of the shaped portion to retain the shaped portion within the sleeve. The shaped portion may have a tapered shape. The pin may be positioned within the sleeve by passing it through the bushing, which expands the bushing.
For simplicity""s sake, as used herein the words xe2x80x9ctubexe2x80x9d or xe2x80x9ctubularxe2x80x9d are used with the intention of encompassing a hollow structure of any shape, whether cylindrical or not.